getuid, geteuid − get user identity
getuid() returns the real user ID of the calling process.
geteuid() returns the effective user ID of the calling process.
These functions are always successful.
POSIX.1-2001, POSIX.1-2008, 4.3BSD.
In UNIX V6 the getuid() call returned (euid << 8) + uid. UNIX V7 introduced separate calls getuid() and geteuid().
The original Linux getuid() and geteuid() system calls supported only 16-bit user IDs. Subsequently, Linux 2.4 added getuid32() and geteuid32(), supporting 32-bit IDs. The glibc getuid() and geteuid() wrapper functions transparently deal with the variations across kernel versions.
getresuid(2), setreuid(2), setuid(2), credentials(7)
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